Kim Eun-Ha, Li Xiao-Ping, Razeghifard Reza, Anderson Jan M, Niyogi Krishna K, Pogson Barry J, Chow Wah Soon
School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT 0200, Australia.
Biochim Biophys Acta. 2009 Aug;1787(8):973-84. doi: 10.1016/j.bbabio.2009.04.009. Epub 2009 May 3.
The multiple roles of light-harvesting chlorophyll a/b-protein complexes in the structure and function of Arabidopsis chloroplasts were investigated using two chlorophyll b-less mutants grown under metal halide lamps with a significant far-red component. In ch1-3, all six light-harvesting proteins of photosystem (PS) II were greatly decreased; in ch1-3lhcb5, Lhcb5 was completely absent while the other five proteins were further decreased. The thylakoids of ch1-3 were less negatively-charged than the wild type, and those of ch1-3lhcb5 were even less so. Despite the expected weaker electrostatic repulsion, however, thylakoids in leaves of the mutants were not well stacked, an effect we attribute to lower van der Waals attraction, lower electrostatic attraction between opposite charges, and the absence or instability of PSII supercomplexes and peripheral light-harvesting trimers. The quantum yield of oxygen evolution in leaves decreased from 0.109 (wild type) to 0.087 (ch1-3) and 0.081 (ch1-3lhcb5) O(2) (photon absorbed)(-1); we attribute this decrease to an excessive spillover from PSII to PSI, a limited PSII antenna, and increased light-independent thermal dissipation in PSII in the mutants. Destabilization of the donor side of PSII, indicated by slower electron donation to the redox-active tyrosine Y(Z)(*) in ch1-3, probably enhanced PSII susceptibility to photoinactivation, increased the non-functional PSII complexes in vivo, and further inactivated PSII complexes in vitro. The evolution of chlorophyll b-containing chloroplasts seems to fine-tune oxygenic photosynthesis.
利用在具有显著远红光成分的金属卤化物灯下生长的两个叶绿素b缺失突变体，研究了捕光叶绿素a/b蛋白复合体在拟南芥叶绿体结构和功能中的多重作用。在ch1 - 3中，光系统（PS）II的所有六种捕光蛋白都大幅减少；在ch1 - 3lhcb5中，Lhcb5完全缺失，而其他五种蛋白进一步减少。ch1 - 3的类囊体负电荷比野生型少，ch1 - 3lhcb5的类囊体负电荷更少。然而，尽管预期静电排斥较弱，但突变体叶片中的类囊体并未很好地堆叠，我们将这种效应归因于较低的范德华吸引力、相反电荷之间较低的静电吸引力以及PSII超级复合体和外周捕光三聚体的缺失或不稳定性。叶片中氧气释放的量子产率从0.109（野生型）降至0.087（ch1 - 3）和0.081（ch1 - 3lhcb5）O₂（光子吸收）⁻¹；我们将这种下降归因于从PSII到PSI的过度溢出、有限的PSII天线以及突变体中PSII中与光无关的热耗散增加。ch1 - 3中向氧化还原活性酪氨酸Y(Z)*的电子供体较慢，这表明PSII供体侧不稳定，可能增强了PSII对光灭活的敏感性，增加了体内无功能的PSII复合体，并进一步使体外的PSII复合体失活。含叶绿素b的叶绿体的进化似乎对氧光合作用进行了微调。
